In apparatus such as disclosed in the above noted patent an electronic particle counting device operating on the Coulter principle is combined with an optical hemoglobinometer such that at some step in the sequence of events of the operation of the counting device, the operation of the optical hemoglobinometer is started. The same sample suspension that is utilized in the counting device is also utilized in the hemoglobinometer by means of a fluid connection from the counting device to the hemoglobinometer so that there is no need to handle the sample twice.
The electronic particle counting device includes an aperture tube such as is commonly known in the art. The fluid connection to the hemoglobinometer is, in the above identified patent, by means of a thief, hereinafter termed a thief conduit. In operation, a liquid suspension of particles is placed in a beaker which is brought into contact with the aperture tube and thief conduit. When the analysis of the liquid supsension is complete, the beaker with remaining liquid suspension is removed and another beaker with a new liquid suspension to be analyzed is brought into contact with the aperture tube and thief conduit so that the analyzing cycle can be repeated.
When the first beaker is removed, a small amount of the liquid suspension can adhere to the exterior surface of the aperture tube and thief conduit. This small amount of liquid suspension will carry over to the liquid suspension in the next beaker, slightly contaminating that liquid suspension and possibly affecting the results of the analysis process. Minimizing this carry over would be extremely desirable.
If the thief conduit draws suspension from the same height in the suspension as the aperture in the aperture tube, it can be assumed that the particles being counted are substantially the same as those being passed through the optical hemoglobinometer. As a result, the probability of a correct analysis is statistically increased. Much time and effort must be spent by a technician to properly align the aperture tube and thief conduit so that when liquid suspension is brought into contact with the aperture tube and thief conduit, they will be at the same height in the liquid suspension. Furthermore, the apparatus must be regularly checked to ensure continued proper alignment, causing a continued expenditure of effort on unproductive activity.
If the aperture tube and thief conduit are positioned at the same height in a suspension, the draw of fluid by the thief conduit can disturb the fluid adjacent the aperture in the aperture tube. if the fluid is disturbed the particle count can be adversely affected. The technician, in setting up the equipment, must exercise great care to ensure that the aperture tube and thief conduit are positioned so as to reduce the possibility of one affecting the operation of the other. Again, there is a continued expenditure of time and effort on what can be considered unproductive activity.